Recording density of the magnetic disk apparatus increases rapidly from year to year, which in turn brings about necessarily a demand for reduction in the flying height of the magnetic head. FIG. 10 is a view for illustrating a flying state of a magnetic head, wherein a magnetic head 1 includes a floating surface 2, a tapered portion 4, a magnetic element 5, an air-stream entrance end 7 and an air-stream exit end 8 and is supported by a leaf spring 10. The floating surface 2 is formed with rails 3. When a magnetic disk is not rotated, the magnetic head 1 and the magnetic disk 11 are placed in the state where they are in contact with each other. When a rotation speed of the magnetic disk has attained a predetermined value, an air bearing slider mechanism is formed by an air stream 40 entering from the air-stream entrance end 7, flowing along the rails 3 and leaving the head from the air-stream exit end 8, whereby a floating force is generated and thus the flying height 12 is determined by coaction of a push-down force exerted by the leaf spring 10 an the floating force. It is one of the important problems to decrease not only the flying height 12 but also variation or difference in the flying height ascribable to difference between the peripheral velocities of inner and outer peripheries of the magnetic disk.
FIG. 11 is a view showing a conventional magnetic head slider known heretofore and a processing method for the same. The conventional magnetic head slider is provided with linear rails 3 which are formed heretofore by a machining process carried out by using a grinding wheel 27. FIG. 14 shows relations between the peripheral velocity and the flying height. In the case where the linear rails are employed, the flying height is within a range of ca. 140 to 200 nm when the disk is operated at the peripheral velocity ranging from 15 to 35 m/s, wherein difference of the flying height between the inner and outer peripheries of the disk amounts to ca. 60 nm, which means that the flying height has a great dependency on the peripheral velocities. Furthermore, in the case where the linear rails are employed, the width of the rail and the flying height bear a proportional relation to each other, and it is desirable to decrease the rail width in order to reduce the flying height. However, in the portion at which the magnetic elements 5 are formed, as can be seen in FIG. 11, the rail width needs to accommodate the width of the magnetic element 5. Consequently, limitation is necessarily imposed onto the diminution of the rail width.
Such being the circumstances, an inclined surface referred to as the chamfered portion is formed at each of corner portions of the rails 3 along which the aforementioned air stream flows in an effort to realize reduction of the flying height as well as suppression of the variation thereof, as is disclosed in U.S. Pat. No. 4,673,996. The inclined surface is so implemented that the angle formed relative to the floating surface is from 0.5 degree to 2 degrees and that the ratio of the area occupied by the chamfered portion to the area of the rail is from 12.5 to 22.5%. As an example of the chamfered portion, there can be mentioned one having a width on the order of 10 .mu.m and a height of 2 .mu.m.
Furthermore, by decreasing the width of a portion of the rail 3, reduction of the flying height as well as suppression of the variation thereof is realized, as is disclosed in Japanese Unexamined Patent Application Publication No. 103406/1988. Additionally, by providing at a corner portion of the rail 3 along which the air stream flows an inclined surface having a width increasing gradually from the entrance end toward the exit end, reduction of the flying height as well as suppression of the variation thereof is realized, as is disclosed in Japanese Unexamined Patent Application Publication No. 188479/1992. By providing the chamfered portion in this manner, the flying height can be reduced so as to fall within a range of ca. 80 to 120 nm at the peripheral velocity of 15 to 35 m/s and at the same time the variation or difference in the flying height between the inner and outer peripheries of the disk is suppressed to ca. 40 nm.
In recent years, as the most effective means for reducing the flying height, there are increasingly adopted a method of using the rails of non-linear shape, as is disclosed in Japanese Unexamined Patent Application Publication No. 276367/1992. An example of the magnetic head having the non-linear rails is shown in FIG. 12. In the case where the non-linear rails of this type are employed, the flying height can be suppressed to a low level within a range of ca. 60 to 75 nm when the disk is operated at the peripheral velocity ranging from 15 to 35 m/s, wherein difference of the flying height between the inner and outer peripheries of the disk is reduced to ca. 15 nm, as can be seen in FIG. 14. The rails of the non-linear shape can ensure the flying height reducing effect equivalent to or more than that attained by the structure in which the chamfered portion is formed in the linear rail, as described above, and is very effective particularly for suppressing the variation of the flying height ascribable to the difference in the peripheral velocity between the inner and outer peripheries of the disk. Accordingly, by forming the chamfered portion in the rail of the non-linear shape which by itself exhibits the desired effect equivalent to or more than the linear rail provided with the chamfered portion, it is expected that the floating characteristic can further be enhanced. Thus, in view of the flying height and the excellent stability as realized, it is necessarily required to distinguish strictly the rail of the linear shape provided with the chamfered portion and the rail of the non-linear shape provided with the chamfered portion from each other. In the current state of the art, the structure in which the rail of the non-linear shape is provided with the chamfered portion is not known. By employing the rail of the non-linear shape, there can be achieved sufficiently the effects of reducing the flying height and suppressing the variation of the flying height, and it is expected that the floating characteristic can further be improved by providing a minute chamfered portion, which in turn however means that realization of optimal geometry of the chamfered portion requires fine and high-precision process when compared with the head having the rails of the linear shape.
In addition to the floating characteristic improving effect described above, provision of the chamfered portion can provide the additional effects mentioned below, as disclosed in Japanese Unexamined Patent Application Publication No. 9656/5198. As can be seen in FIG. 10, the flying height at the air-stream exit end 8 is small when compared with the flying height at the air-stream entrance end 7, and thus the air-stream exit end 8 is more likely to contact the magnetic disk 11. For this reason, it is desired that the geometry of the air-stream exit end 8 of the magnetic head 1 be smooth for protecting not only the magnetic disk 11 but also the magnetic head itself against injury. To this end, the chamfered portion is provided. In order to realize the effects mentioned above with the rails of the non-linear shape, there is demanded realization of the non-linear rails strictly with high precision as described hereinbefore in conjunction with the effect affecting the floating characteristics.
A process for fabricating a magnetic head having rails of non-linear shape will be elucidated by reference to FIG. 13. After forming the magnetic element 5 in a substrate of the alumina titanium carbide 13, a typical substrate material, the substrate is cut into head blocks 14 each including a plurality of sliders, whereon the floating surface 2 is formed by grinding or polishing to a predetermined dimension (a), a protecting film 15 is formed on the floating surface by sputtering, CVD or the like process (b), resist 16 serving as a mask for forming the rails is applied, a resist pattern is formed through lithography (c), rails are then formed on the floating surface through an etching process (d) and (e), and the product is then cut into individual sliders (f) to realize magnetic heads 1' such as shown in FIG. 12. Because the step (d) of forming the rails on the floating surface can not be carried out by the conventional machining process using a grinding wheel due to the non-linear shape of the rail, there is ordinarily adopted the etching process such as reactive ion etching, plasma etching, sputter etching and ion milling etching process. Since alumina titanium carbide forming the substrate has a very low reactivity with the etching gas, the etching process is realized primarily by resorting to a physical removal effect based on high-energy ion impact. Consequently, all the particulates sputtered by the physical etching are not always sucked into the vacuum pump but some part of the sputtered particulates is deposited on the mask material and side walls of the alumina-titanium-carbide substrate, as is illustrated in FIG. 5 at (a). This phenomenon will be referred to as the re-deposition. The re-deposited particulates 19 remain in the form of projections even after the removal of the resist 16 serving as the mask, as shown in FIG. 5 at (b). To remove such re-deposition, there is disclosed in Japanese Unexamined Patent Application Publication No. 109668/1993 a method of eliminating the re-deposition by changing the angle at which an argon ion beam impinges onto the substrate during the processing, as is disclosed in Japanese Unexamined Patent Application Publication No. 109668/1993. According to this method, the etching process is carried out at first with the argon ion beam with the angle of incidence which is not greater than 5 degrees and subsequently the re-deposited particulates are removed by setting the angle of incident of the ion beam at least at 30 degrees. Further, in Japanese Unexamined Patent Application Publication No. 13357/1994, there is disclosed a method of removing the re-deposited particulates by carrying out an isotropic plasma etching in succession to the ion milling process.
When the re-deposition takes place in the course of processing of the magnetic head slider, the re-deposited particulates will remain on the floating surface of the slider rail of the magnetic head notwithstanding of removal of the mask material after the etching process, giving rise to problems that the magnetic disk may be injured by the re-deposited particulates upon starting and stopping of the magnetic head, the re-deposited particulates may fall during operation of the magnetic disk apparatus, providing a cause for fault and so forth. Besides, in view of the fact that the flying height decreases from year to year, the height of the re-deposition as measured from the floating surface may become comparable to the flying height, exerting severe influence to the very floating performance of the magnetic head. Under the circumstances, there has arisen a demand for development of the process for the elimination of the re-deposition.
Although the conventional method of eliminating the re-deposition by changing the angle of incidence of the argon beam as described hereinbefore is one of the most effective methods for the elimination of the re-deposition, it is impossible to eliminate the re-deposition in the etching process carried out by resorting to the ion milling or the like of ceramics such as alumina titanium carbide, the typical material for the substrate of the magnetic head slider, the reason for which will be described below. Referring to FIG. 21, formation of the re-deposition will be described in the case where the ion milling process is performed for the alumina-titanium-carbide substrate by using an argon gas with a resist being used as the mask material. FIG. 21 is a conceptual view illustrating the formation of the re-deposition, in which reference numeral 16 denotes the resist, 13 denotes an alumina-titanium-carbide substrate, 19 and 19a denote re-deposited particulates, and 39 denotes an ion beam. When the resist 16 and the alumina-titanium-carbide substrate 13 are irradiated with the ion beam, emission of fine particles or particulates of respective materials takes place under the effect of bombardment of ions. Some of the fine particulates as emitted are suspended in the atmosphere within the vacuum chamber to be ultimately discharged into a vacuum pump, while some of the particulates collide against the surfaces of the resist and the alumina-titanium-carbide substrate. Some of the fine particles or particulates colliding against the surfaces of the resist and the alumina-titanium-carbide substrate will remain on these surfaces, being deposited, while some of the fine particulates will be emitted again, wherein the probability of the deposition depends on the processing conditions such as energy of the ion beam, species of the materials to be processed and others. It is believed that in the case of the process in which the ion beam of high energy is employed as in the case of the ion milling, the deposition likelihood is high, approximating to 1 (one). Consequently, in the course of the processing, fine particles or particulates of the alumina-titanium-carbide substrate or the resist or mixture of these two materials will constantly exist, being deposited on the surfaces of the resist and the alumina-titanium-carbide substrate.
At this juncture, ion milling rates for alumina titanium carbide and the resist are illustrated in FIG. 22. The ratio of the ion milling rate for the resist to the ion milling rate for the alumina-titanium-carbide substrate (hereinafter this ratio will be referred to as the selection ratio) lies within a range of ca. 0.3 to 0.5, although this ratio will change in dependence on the angle of incidence of the ion beam, which means that the processing rate for the resist is always as high as twice to three times of the processing rate for alumina-titanium-carbide substrate. Consequently, when the re-deposited particulates 19 of alumina titanium carbide adhere to the side wall of the resist, as can be seen in FIG. 21, the portion of the resist covered by the re-deposited particulates 19 undergoes the ion milling at lower rate when compared with the surrounding resist portion, resulting in formation of concave/convex surface. When deposition of the fine particles or particulates on the concave/convex surface is repeated, a re-deposition layer is formed, as can be seen in FIG. 5 at (a).
Since the method described above is so designed as to eliminate the re-deposition by increasing the energy of the ion beam incident on the side walls of the resist and the material being processed by changing the angle of incidence of the ion beam, it must be possible to increase the incidence angle of the ion milling on the way of the ion milling for processing the alumina-titanium-carbide substrate. When the incidence angle of the ion beam is selected greater than 60 degrees inclusive, the rate at which the re-deposited particulates on the side walls are etched becomes higher than the rate at which the re-deposition occurs on the side walls. Accordingly, the re-deposited particulates must theoretically be removed. However, in the case of the processing for the alumina-titanium-carbide substrate, concaves/convexes, i.e., roughness such as illustrated in FIG. 23 at (b), make appearance in the side wall, because of significant difference in the processing rate between the alumina-titanium-carbide substrate and the resist, as descried hereinbefore. The re-deposited particulates 19a adhering to the concave portions forming in part the roughness can never be removed because the re-deposited particulates are not exposed to the ion beam unless the incidence angle of the ion beam is set at 90 degrees or more. However, when the incidence angle of the ion beam is set higher than 90 degrees inclusive, the whole side walls will then be located within a shadow area of the resist, being not exposed to the ion beam. Consequently, the ion beam can not impinge onto the side wall. Such processing conditions are impracticable.
The roughness of the side wall can be explained by the fact that the selection ratio between the resist and the alumina-titanium-carbide substrate is poor. If this selection ratio is on the order of 1 (one), neither the roughness nor the re-deposition can take place. However, at present, the resist permitting such low processing rate which is substantially equal to that of alumina titanium carbide is unavailable. In the conventional alumina titanium carbide processing known heretofore, the incidence angle of the ion beam is initially set at 45 degrees with the processing rate also being set high, and when the processing proceeds to the state approaching a desired processed state, the incidence angle is set at 75 degrees for performing the removal of the re-deposited particulates. When the processing is performed with the incidence angle set at 45 degrees, a significant amount of the re-deposited particulates can be observed on the side walls of the resist and the alumina-titanium-carbide substrate, as is shown in FIG. 23 at (a), while in the processing with the incidence angle of the ion beam set at 75 degrees, a large part of the re-deposited particulates can be removed, as is illustrated in FIG. 23 at (b). However, for the reason mentioned hereinbefore, some part of the re-deposited particulates will yet remain in the adhering state, and even after the removal of the resist, a very small amount of re-deposited particulates continues to remain unremoved, as is illustrated in FIG. 23 at (c). The minute amount of re-deposition which can not be eliminated even when the incidence angle of the ion beam is changed in the ion milling process presents a serious problem, and there exists a demand for developing the method capable of removing the minute amount of re-deposited particulates.
On the other hand, the method of eliminating the re-deposition by resorting to the use of isotropic plasma etching is primarily for a thin-film process and effective for a semiconductor process for which a relatively small amount of processing is required. However, the amount of processing involved in fabrication of the magnetic head slider is large and at the same time the amount of the re-deposition is equally large. Thus, the above-mentioned method takes an increased time for forming the magnetic head slider. Besides, it is noted in conjunction with the magnetic head slider that the rail width and the groove depth bear close relation to the flying height. Consequently, very severe precision requirement is imposed on the processing. In this conjunction, it is noted that with the isotropic etching process which allows a relatively large amount of material to be etched away from the side wall, not only variation in size but also in the shape is remarkable. Thus, the isotropic etching process can not be applied for forming the magnetic head slider.
Thus, there exists a demand for developing a re-deposition eliminating method which is capable of eliminating completely the re-deposition not only from the floating surface but also from the side wall portions of the rails and which can assure negligibly small dimensional deviations of the rail.
By adopting the rails of the non-linear shape, the flying height can be reduced and at the same time variation or difference in the flying height ascribable to the difference in respect to convergence degree between the inner and outer peripheries of the magnetic disk can be mitigated. However, for further enhancing or improving the floating characteristics, it is preferred to form an extremely chamfered portion at the corner portion of the rail. Besides, in order to mitigate the shock which may occur upon starting/stopping of the magnetic disk rotation, it is desirable to form the chamfered portion at the air stream exit end as well. The size of these chamfered portions is small on the order of one tenth of the chamfered portion formed in the rail of the linear shape in the conventional magnetic head, which requires extremely high processing precision. In the linear-shaped rail of the magnetic head known heretofore, such chamfered portion is formed by resorting to grinding and tape polishing. However, in the case of the rail of the non-linear shape, such processing techniques will encounter great difficulty in forming the chamfered portion. Such being the circumstances, there also exists a demand for developing a processing technique for forming the chamfered portion in the rail of the non-linear shape with high precision or accuracy.